Rats lesioned in the dorsal hippocampus (HL) or in the overlying parietal cortex (CL) show poorer memory for a discriminated avoidance task than sham operated controls when tested 21 days after training. HLs learn the task faster than CLs or shams and all groups perform maximally when tested 24 hours after acquisition. The present investigation has three objectives: (1) To determine if the HL alone produces the memory deficity, or if the previous results were due to concomittant cortical damage in HLs. (Expt. I) (2) To examine under what conditions and to what extent the memory deficity can be alleviated. We are testing the hypothesis that these memory deficits are due to retrieval failures, which can be reversed at least in part, by pre-test manipulation of the external or the internal environment of the animal. In Expt. II, contextual cues are presented prior to the retention test, in an attempt to facilitate retrieval. Pre-test contextual cues have been shown in other experiments to reverse amnesias and spontaneous forgetting in intact rats. Expt. III examines the effect of electrical stimulation of the mesencephalic reticula formation (MRF) immediately before retention test on retrieval of the discriminative avoidance response. Our previous work has shown this to be an effective retrieval facilitator in intact rats in a spatially discriminated approach task. The results will be discussed in terms of therapeutic possibilities in individuals with memory disorders due to the neurological damage associated with ageing, alcoholism and stroke.